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New Tools Illustrate a Technique for Large-Scale Storage of Renewable Energy

A new approach based on the principles of NMR and MRI has facilitated researchers noticing the way next-generation batteries function for major energy storage, as well as how they fail. This observation will help them in the advancement of plans to extend the lifetime of batteries, helping to work towards a zero-carbon future.

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These new tools developed by researchers based at the University of Cambridge will help design safer and more efficient battery systems for grid-scale energy storage. Additionally, the method may also be employed in different kinds of electrochemical cells and batteries to unravel the complicated reaction mechanisms that take place in these systems and to detect and diagnose faults.

The scientists tested their techniques on organic redox flow batteries, which were best suited to store sufficient renewable energy to power cities and towns. Still, this energy would degrade too rapidly for commercial applications.

The researchers identified that by charging the batteries at a lower voltage, they were able to considerably decrease the rate of degradation, thus extending the lifespan of batteries. The study results have been published in the Nature journal.

Apart from fossil fuel-based energy sources, batteries are an essential piece of the transition. Without batteries that have the ability for grid-scale storage, it will not be feasible to boost the economy relying only on renewable energy.

Furthermore, lithium-ion batteries that are appropriate for consumer electronics do not scale-up readily to store enough energy to power an entire city. Additionally, the flammable materials contained in lithium-ion batteries cause potential safety risks. The bigger the size of the battery, the more potential damage could be caused in the event of a fire.

One of the possible solutions to resolve this technological puzzle is redox flow batteries. They include two tanks filled with electrolyte liquid, one positive and one negative, and can be scaled up simply by increasing the tank’s size. This makes them well suited for storing renewable energy. These building-sized or room-sized non-flammable batteries may play a major role in the future green energy grid.

Redox flow batteries are developed by many companies at present for commercial applications. Vanadium is mostly used as the battery's electrolyte. Although vanadium is toxic and costly, battery researchers are working to create a redox flow battery based on long-lasting and inexpensive organic materials. However, these molecules have a tendency to degenerate rapidly.

Since the organic molecules tend to break down quickly, it means that most batteries using them as electrolytes won’t last very long, making them unsuitable for commercial applications. While we’ve known this for a while, what we haven’t always understood is why this is happening.

Dr Evan Wenbo Zhao, Study First Author, Department of Chemistry, University of Cambridge

At present, Zhao and his co-workers in Professor Clare Grey’s research group in Cambridge, together with collaborators from the Spain, United Kingdom, and Sweden, have created two novel techniques to study in-depth the organic redox flow batteries. This would help to recognize why the electrolyte breaks down, as well as to enhance their performance.

By utilizing “real-time” nuclear magnetic resonance (NMR) studies, a sort of functional “MRI for batteries,” and methods developed by Professor Grey’s group, the scientists were able to read resonance signals from the organic molecules, both in their original states and when they degraded into other molecules.

These “operando” NMR studies of the self-discharge and degradation in redox flow batteries offer better understanding into the internal and fundamental mechanisms of the reactions, like electron transfers between the numerous redox-active species in the solutions, and radical formation.

There are few in situ mechanistic studies of organic redox flow batteries, systems that are currently limited by degradation issues. We need to understand both how these systems function and also how they fail if we are going to make progress in this field.

Clare Grey, Professor, Department of Chemistry, University of Cambridge

The scientists were able to discover that the organic molecules had a tendency to degrade more rapidly under certain conditions.

If we change the charge conditions by charging at a lower voltage, the electrolyte lasts longer. We can also change the structure of the organic molecules so that they degrade more slowly. We now understand better why the charge conditions and molecular structures matter.

Dr Evan Wenbo Zhao, Study First Author, Department of Chemistry, University of Cambridge

Currently, the scientists intend to implement their NMR set-up on different types of organic redox flow batteries, and also on alternative kinds of next-generation batteries, like lithium-air batteries.

Grey added, “We are excited by the wide range of potential applications of this method to monitor a variety of electrochemical systems while they are being operated.”

For instance, the NMR technique will be utilized to create a portable battery “health check” device to diagnose its condition.

Using such a device, it could be possible to check the condition of the electrolyte in a functioning organic redox flow battery and replace it if necessary. Since the electrolyte for these batteries is inexpensive and non-toxic, this would be a relatively straightforward process, prolonging the life of these batteries,” added Zhao.

The study was partially supported by the Engineering and Physical Sciences Research Council (EPSRC) and Shell.


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